The objective of this project is to gain some understanding of the role of two early functions of polyoma virus in transformation: the hr-t function and the ts-a function. Complementation between the two classes of transformation defective mutants representing the two functions governs different steps of transformation. This project deals with the analysis of the properties of transformed clones obtained by complementation, referred to as complementation clones. Of particular interest is the question of which viral genes are required to be persistently expressed in complementation clones, and what their relative topology in the host cell is. The method involves the analysis of rescued virus, of the viral integration and of the proteins produced in the transformed cells.